1. Field of Invention
This invention relates generally to hypodermic syringes, and in particular to a safety hypodermic needle and shield assembly for a hypodermic needle to permit its use, the assembly when unlatched assuming an extended mode in which the shield protectively covers the point of the needle to prevent accidental sticks thereby.
2. Status of Prior Art
A hypodermic needle is usable for intravenous, subcutaneous and intramuscular injection of fluids, or the removal of blood (venipuncture), body fluids or abnormal collections thereof, the needle being of hollow construction and having a slanted open point. When the needle is mounted on a syringe, it is adapted to aspirate or inject fluids for diagnostic or therapeutic purposes.
Disposable hypodermic needles are now mass produced at low cost, many billions of such syringes being used every year in the health care field. While the modern hypodermic syringe now includes a fluid chamber molded of synthetic plastic material rather than glass, the basic design of this widely used medical appliance remains much as it was in 1853 when it was invented by Charles Pravaz, a French physician.
In a hypodermic syringe of standard design, a piston is slidable within a cylindrical fluid chamber, the shank of the piston extending beyond the open rear end of the cylinder and terminating in a handle. The front end of the chamber is provided with a projecting nozzle that is coaxial with an internally-threaded socket adapted to receive a needle-supporting hub. When the hub is screwed into the socket, the nozzle is then received therein to communicate with the needle.
A hypodermic needle and a syringe attached thereto are distributed in sterile condition within a plastic bubble package and to protect them against contamination in storage and shipment. In addition, the needle is enclosed in a removable overcap whose inlet end snaps onto the needle hub. Thus, after the hypodermic needle and syringe are removed from its package, in order to put it to use one must first remove the overcap to expose the needle. After the hypodermic syringe has been injected into a patient and then withdrawn, it is the usual practice before discarding the syringe to place the overcap back on the needle hub so that those thereafter handling discarded syringes for purposes of disposal will not be pricked thereby.
When a sterile hypodermic needle is injected into a patient suffering from hepatitis or other infectious disease, when the needle is then withdrawn from the patient, it may be contaminated with infectious agents. Hence, should the handler inadvertently prick himself with this contaminated needle, the consequences may be serious.
The possibility of accidental contamination by needle puncture of the skin of those individuals in the health care field who employ hypodermic syringes for venipuncture, the withdrawal of body fluids or for any other medical purpose is fairly high and represents a significant risk. Thus, physicians, nurses, laboratory personnel, paramedics and other involved in the care and treatment of patients are in danger of being accidentally inoculated with infectious microorganisms by contaminated needles.
Most accidental needle sticks occur when the needles are being recapped; for to do so properly, one must first align the needle with the relatively small diameter inlet of the overcap. Should the needle be misaligned, as may well happen should the handler be careless, distracted or fatigued, the point of the needle will not enter the overcap but may instead puncture the finger of the handler.
It is well established that in the last 25 years the risks involved in handling hypodermic syringes has markedly increased. Statistics indicate very high rates of hepatitis B infection among medical and laboratory personnel by reason of this accidental mode of disease transmission. The results of positive hepatitis surface antigen testing reveals a five-to-fifteen fold increase in the risk of developing the antigen and antibody (as well as chronic hepatitis) among surgeons and other health care personnel dealing with patients belonging to high risk groups, such as patients undergoing renal dialysis, drugicts, and the like. In a recent issue of the newsletter, Biomedical Business International, it is reported that there are between 800,000 and one million accidental needle sticks each year.
Medical personnel who care for patients suffering from AIDS run a still higher risk; for a needle contaminated with HIV (Human immunodeficiency virus) is a source of great danger. Should the handler of this needle be accidentally punctured, he faces the prospect of contracting a disease currently having a 100% mortality rate as compared, say, to the 5 to 10% mortality rate for hepatitis B.
Yet, in the prior art, it was only in recent years that patents have issued dealing with expedients to prevent accidental needle sticks. Thus, the expired patents Bauer, U.S. Pat. Nos. 2,674,246; White, 2,876,770; Saenz, 3,046,985; and Armao, 3,134,380, through dealing with hypodermic syringes are mainly concerned with the fact that most patients are frightened by the mere appearance of a hypodermic syringe. Patients object to being punctured by a sharp needle, even though it is a relatively painless experience. To overcome this fear, these patents provide a guard to conceal the needle so that it is never seen by the patient, even as he is being injected. Thus, the White patent provides a spring-biased guard which normally covers the needle. But when the needle is injected in a patient, the nose of the guard presses against the tissue and the spring is compressed to permit the needle to project out of the guard into the tissue.
The 1988 patent to Wanderer et al., U.S. Pat. No. 4,731,059, is concerned with preventing needle sticks, and for this purpose provides a shield which is slidable from a position covering the needle to a position overlying the fluid chamber so that the needle can be exposed when put to use and thereafter shielded. A somewhat similar arrangement is disclosed in the 1987 patent to Fox, U.S. Pat. No. 4,695,274, which shows a retractable safety jacket for a hypodermic needle.
One practical problem with the safety shields or needle guards of the type disclosed in the Wanderer et al. and Fox patents is that when the needle is exposed so that the syringe can be put to use, the retracted guard then covers and obscures the transparent chamber which is graduated so that one can determine the amount of fluid that is contained therein. Hence this guard interferes with the proper operation of the hypodermic syringe.
But the more serious drawbacks of prior art needle guard arrangements is that they require a modification of the basic configuration of the standard hypodermic syringe to accommodate the guard. Thus in one commercially-available form of safety hypodermic syringe, in order to accommodate a needle guard, the needle is mounted on an elongated extension rod projecting from the fluid chamber, so that when the guard is retracted, it overlies the extension rod, not the fluid chamber. Hence, fluid from the chamber must be conducted through the extension rod which by its very nature elongates the hypodermic syringe, making it more difficult to handle. Also, the extension tube will retain and waste an excessive amount of fluid.